Field of the Invention
The invention of the instant application relates to a chill roller for use in the graphic arts industry, in particular for cooling a printed web of material in a rotary printing press.
U.S. Pat. No. 4,920,881 discloses a method of cooling hot webs of material. This disclosure is related to a method for cooling a hot web by passing it across a rotating thermally conductive chill roller having a recirculating coolant therein. In accordance with U.S. Pat. No. 4,920,881, a liquid refrigerant at a temperature and pressure permitting the refrigerant to exist in liquid form is introduced as a coolant to the chill roller, the temperature being also above the dew point of the ambient atmosphere. Likewise, the boiling point of the refrigerant at the desired temperature and pressure is low enough to cause heat to be absorbed by the chill roller primarily by vaporization of the liquid refrigerant. Refrigerant vapor is then withdrawn from the chill roller and is typically refrigerated to reform the liquid phase for return to the chill roller. Typically, chlorofluorcarbon refrigerants are preferred.
The published European Patent Document EP 0 468 219 A1 discloses a chill stand within which a plurality of chill rollers are mounted in a chill roller stand. Wit h this construction, boundary layers of ambient air and oil vapor adhering to both sides of the passing web of material are dissipated while the web of material moves through the chill stand. The chill rollers are mounted on frames, which can be adjusted with respect to one another. By a movement of the respective frames, the chill roller adopts positions in which portions of the moving web being transported in opposite directions around respective chill rollers are kept at a narrow distance from one another to create a boundary layer destroying zone. The boundary layer adhering to those portions of the web of material kept at a narrow distance with respect to one another are dissipated within the boundary layer dissipating zone.
The published European Patent Document EP 0 346 046 A2 discloses a chill roller. This document relates to a chill roller for cooling a web, a printed web of material such as in the graphic arts industry, where a uniform temperature across the chill roller is maintained. Journals support an outer roller assembly and an inner roller assembly. The inner roller assembly is bearing mounted on the inner ends of opposing journals and the outer roll is rotated about the inner roller, which is weighted to free-wheel about the bearings to minimize rotary motion. Coolant is introduced through the journal on one end and into a center tube, where the coolant uniformly flows in an annular space between the rollers and along the length of the inner and outer roller assemblies to circumferentially traverse between the rotating and stationary outer and inner rolls. This coolant flow provides enhanced heat transfer from the outer rotating chill roller to the circulating coolant. Heated coolant collects and returns through a center tube and exhausts through the center tube and out through the journal. Turbulence inducer bars between the inner and outer roller assemblies create a turbulence in the coolant flow between the outer and inner rollers to further enhance heat transfer.
Heretofore, double wall steel cooling rollers with and without a spiral have been in use. The spiral has been constructed to move the water at an even rate between the outer and the inner wall of a cooling roller. However, despite the use of the spiral with the cooling roller, there still remains the problem of an inhomogeneous heat transfer on a cooling roller causing the significant problem of a web drift due to changes, even slight changes, in the diameter of the chill rollers caused by temperature differences. Furthermore, the provided solution of double wall cooling rollers offers little or no possibility at all for a temperature adjustment.
Efforts have been made to ease the major drawbacks of the aforementioned double wall cooling rollers by having a plurality of cooling water circuits connected to the chill roller stand to provide coolants with a different temperature level. Additionally, cooling water bypasses have been constructed having a pump or three-way valves and the corresponding bypass-piping systems. The additional costs involved with these efforts and the outcome thereof have not justified the approaches taken to address the problem in this manner.